1873-] New Facts concerning the Diamond. 449 



and that the interior had undergone no alteration : the 

 blackened fragments could be used for writing on paper. 

 From these experiments, and also from the one described 

 above in which the surface of the diamond had turned black 

 after exposure in a crucible of charcoal to heat capable of 

 melting wrought-iron, the conclusion drawn by M. Rose is, 

 that under the influence of excessively high temperatures, 

 the diamond, although preserving its shape, begins to 

 change into graphite, and would probably do so entirely if 

 the heat were sufficiently strong and prolonged for the 

 requisite period. 



Opportunity for a repetition of these experiments, not 

 having occurred to M. von Baumhauer, he has not given an 

 opinion upon the behaviour of diamonds at extremely high 

 temperatures ; it may, however, be remarked that the 

 blackening which occurs when the diamond is placed in the 

 voltaic arc, may result from transmission of carbonaceous 

 particles from the charcoal poles to the surface of the 

 diamond, which would retain them without the occurrence 

 of any radical alteration. During the employment of the 

 burning-glass, the support upon which the diamond was 

 held might possibly contain matter, which on coming in con- 

 tact with the carbon of the diamond at so high a temperatue 

 might give rise to reductive phenomena conducive to the for- 

 mation of the black coating. Something of the kind was observed 

 by M. Schrotter, in an experiment in which the diamond was 

 placed in a crucible in the centre of a mass of strongly 

 compressed magnesia, and moreover folded in a thin sheet 

 of platinum, and then exposed to excessive heat in a por- 

 celain oven. After cooling, the diamond was found to be 

 divested of its platinum cover, which had melted into a 

 globule and adhered to one of its facets. The exterior of 

 the diamond had turned black, whilst its interior was per- 

 meated with black dendritic striae, giving rise to the sup- 

 position that a combination of carbon and platina had 

 occurred. 



Without having employed the extreme heat attainable in 

 the arc of a powerful galvanic battery, or at the focus of 

 a burning-glass of large dimensions, M. von Baumhauer 

 has, nevertheless, more than once heated diamonds in the 

 oxyhydrogen flame (that is to say, to a temperature capable 

 of melting platinum*) in which the stone emitted a brilliant 

 light, and lost weight rapidly ; after the experiment the 



* When the points of the platinum which held the diamond were touched 

 by the flame, not only did they melt, but upon examination through smoked 

 glass the platinum was seen to be in decided ebullition. 



